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| United States Patent |
6,143,837
|
|
Al Ghatta
, et al.
|
November 7, 2000
|
Process for the preparation of polyester resin
Abstract
A process for the preparation of aromatic polyester resins, in which the
resin obtained from the polycondensation phase in the molten state
conducted by utilizing a titanium based compound as a catalyst, is
subjected to a solid state polycondensation reaction in the presence of a
dianhydride of a tetracarboxylic acid.
| Inventors:
|
Al Ghatta; Hussain (Fiuggi, IT);
Ballico; Enrico (Marino, IT);
Giovannini; Arianna (Bologna, IT)
|
| Assignee:
|
Sinco Ricerche, S.p.A. (IT)
|
| Appl. No.:
|
468158 |
| Filed:
|
December 21, 1999 |
Foreign Application Priority Data
| Dec 23, 1998[IT] | MI98A2803 |
| Current U.S. Class: |
525/437; 524/706; 524/711; 524/783; 528/272; 528/279; 528/298; 528/302; 528/308; 528/308.6; 528/487; 528/503 |
| Intern'l Class: |
C08F 020/00; C08G 063/78 |
| Field of Search: |
528/272,279,298,302,308,308.6,486,487,503
525/437
524/706,711,783
|
References Cited
U.S. Patent Documents
| 6057016 | May., 2000 | Al Ghatta et al. | 428/35.
|
Primary Examiner: Acquah; Samuel A.
Attorney, Agent or Firm: Cook, Alex, McFarron, Manzo, Cummings & Mehler, Ltd.
Claims
What is claimed is:
1. A process for the preparation of polyester resins having an intrinsic
viscosity greater than 0.7 dl/g starting from resins with an intrinsic
viscosity of 0.2-0.7 dl/g obtained by polycondensation of diols with 2-12
carbon atoms and aromatic dicarboxylic acids or by transesterification of
the lower alkyl esters of the dicarboxylic acids and subsequent
polycondensation, using in the polycondensation phase a catalyst
comprising a titanium compound, wherein the polyester resin obtained from
the polycondensation is added with a dianhydride of a tetracarboxylic acid
and subsequently subjected to solid state polycondensation to obtain an
intrinsic viscosity increase of at least 0.1 dl/g.
2. A process according to claim 1, in which the titanium compound is
selected from the group consisting of alkoxides of titanium, acetyl
acetonates of titanium, dioxides of titanium and titanate phosphites.
3. A process according to claim 1, in which the dianhydride is the
pyromellitic dianhydride.
4. A process according to claim 1, in which the polyester resin is
polyethylene terephthalate and co-polyethylene terephthalate in which up
to 20% by weight of units deriving from terephthalic acid are substituted
by units deriving from isophthalic and/or naphthalene dicarboxylic acid.
5. A process according to claim 2, in which the polyester resin is
polyethylene terephthalate and co-polyethylene terephthalate in which up
to 20% by weight of units deriving from terephthalic acid are substituted
by units deriving from isophthalic and/or naphthalene dicarboxylic acid.
6. A process according to claim 3, in which the polyester resin is
polyethylene terephthalate and co-polyethylene terephthalate in which up
to 20% by weight of units deriving from terephthalic acid are substituted
by units deriving from isophthalic and/or naphthalene dicarboxylic acid.
7. A process according to claim 2, in which the dianhydride is the
pyromellitic dianhydride.
8. A process according to claim 7, in which the polyester resin is
polyethylene terephthalate and co-polyethylene terephthalate in which up
to 20% by weight of units deriving from terephthalic acid are substituted
by units deriving from isophthalic and/or naphthalene dicarboxylic acid.
Description
BACKGROUND OF THE INVENTION
The present invention is directed to an improved process for the production
of polyester resin having a high intrinsic viscosity.
The catalysts normally used in polycondensation of aromatic polyester
resins in the molten state are in general compounds of antimony
(principally, antimony oxide and antimony triacetate). Catalysts based on
germanium oxide are also usable but only in certain cases, given the high
cost of the catalyst.
Titanium compounds (in particular titanium alkoxides) have also been
proposed as catalysts. These catalysts have a high activity, but lead to
the formation of a polymer with a yellowish colouration and further, have
problems of instability due to hydrolysis during synthesis of PET from
terephthalic acid. The kinetics of polycondensation of the resin to the
solid state is moreover detrimentally affected by the presence of titanium
compounds. Because of these disadvantages, titanium catalysts have not in
practice found to have an application.
Currently, the tendency of the market and the authorities competent for
safeguarding the environment is to require ever more insistently a PET
having a low content of residual metal catalysts. It is not, however, in
practice possible to reduce the quantity of antimony catalysts because
their activity is not very high.
The use of titanium catalysts is not satisfactory because of their low
activity in the solid state polycondensation.
A necessity therefore exists to have available inexpensive catalysts other
than those of antimony, which will not be a health hazard and which will
provide good catalytic activity without presenting possible problems of
colouration of the polymer.
Recently titanium dioxide and silica in the ratio Ti:Si of 9:1, and
tetraisopropyl (dioctyl) titanate phosphite have been proposed as
hydrolysis resistant catalysts having few problems with yellowing when
compared to titanium alkoxides. The activity of these catalysts (expressed
as ppm by weight of Ti/kg polymer) is very much higher than that
obtainable with antimony oxide or triacetate.
These catalysts, however, also have the serious disadvantage in that their
use is, in practice, precluded due to the low kinetics when they are
employed for the solid state polycondensation of the resin.
With respect to antimony catalysts, in the case of PET, the kinetics of
solid state polycondensation are about 50% less (for the same conditions).
SUMMARY OF THE INVENTION AND DETAILED DESCRIPTION OF THE PRESENTLY
PREFERRED EMBODIMENTS
It has now been unexpectedly found that it is possible to utilize titanium
catalysts in the polycondensation reaction of the polyester resin in the
molten state and to obtain kinetics of the solid state polycondensation
comparable and possibly better than those of polymers prepared utilizing
antimony catalysts if the solid state polycondensation is conducted in the
presence of a dianhydride of a tetracarboxylic acid, preferably aromatic.
Pyromellitic dianhydride is preferred. The dianhydrides are added to the
polyester resin in quantities of about 0.05 to 2% by weight.
The solid state polycondensation reaction is effected according to known
methods by operating at a temperature between 160.degree. and 230.degree.
C. for a time sufficient to obtain an increase of at least 0.1 dl/g of
intrinsic viscosity for the starting resin. The viscosity of the starting
resin is in general between 0.4-0.7 dl/g. It is, however, possible to
start from resins with viscosity lower than 0.4 dl/g, for example, 0.2-0.3
dl/g.
The dianhydride is mixed with the resin in the molten state operating, for
example, in extruders with relatively short residence times (several tens
of seconds).
Polycondensation in the molten state of the polyester resin is achieved
according to conventional methods using quantities of titanium catalysts
equal to 20-200 ppm by weight of titanium with respect to the polymer.
Since the catalytic activity of titanium is much higher that that
obtainable with antimony catalysts (less ppm of metal per kg of polymer),
it is possible to reduce the polycondensation times in the melt for the
same ppm of metal used, thus increasing the productivity of the
installation.
Titanium compounds usable as catalysts generally comprise titanium
alkoxides, in particular, titanium tetraethoxy, tetrapropoxy and
tetrabutoxy, and tetraisopropyl (dioctyl) titanate phosphite and the
acetyl acetonates of titanium, such as titanium acetylacetoyl and titanium
diacetyl acetoxide and titanium dioxide-silica mixture.
The polyester resins in the synthesis of which the titanium catalysts are
usable are obtained by polycondensation according to known methods from a
diol with 2-12 carbon atoms and aromatic dicarboxylic acids, preferably
terephthalic acid, or by transesterification of their lower aliphatic
diesters for example dimethyl terephthalate and subsequent
polycondensation. Diols usable are for example ethylene glycol, propylene
glycol, butylene glycol and 1,4-cyclohexanedimethylol.
Preferred resins are polyethylene terephthate and ethylene terephthalic
copolymers in which up to 20% by weight of units deriving from
terephthalic acid are substituted by units of isophthalic and/or
napthalene dicarboxylic acid.
Polyester resins obtainable with the process of the present invention find
application in all fields in which polyester resins are normally used. In
particular, they are used for the preparation of containers by injection
blow moulding or extrusion blow moulding and in the preparation of
expanded materials.
In table 1, there are recorded the polycondensation conditions of
bis-hydroxyethyl terephthalate (BHET), and the results obtained by using a
titanium catalyst (mixture of titanium dioxide and silica; Ti/Si ratio
9:1; C-94 from Akzo Nobel) and an antimony catalyst (antimony triacetate
S21 from Atochem).
TABLE 1
______________________________________
Test With
Test With
Antimony Titanium
______________________________________
Polycondensation 267 267
Temperature (.degree. C.)
(Starting value)
Vacuum (mbar) 1-5 1.0
Polycondensation Time 4h 30' 4h 30'
Final Polycondensation 269 270
Temperature (.degree. C.)
Quantity of Catalyst 240 60
(ppm metal)
Intrinsic Viscosity (dl/g) 0,653 0,673
Activity (IV.sub.f /hrs*ppm Me) 0,002481 0,000602
Activity Ti/Activity Sb 4,123077 --
Terminal Acid Groups Eq/T 13 13.8
Colour
L* 71 76
a* -2.86 -2.48
b* -1.27 4.73
______________________________________
From the data of the table, it is apparent that the titanium catalyst is
four times more active than the antimony catalyst (activity expressed as
increment of intrinsic viscosity per ppm of metal per hour of reaction).
The colour index b* of the polymer obtained with the titanium catalyst is
significantly higher than in the polymer containing the antimony catalyst
(the disadvantage can, however, be easily eliminated by adding to the
catalyst small percentages of a cobalt compound or other organic
colorants).
In table 2 are recorded the I.V. data relating to the solid state
polycondensation (195.degree. C. in a nitrogen current) of the polymer
obtained with the antimony catalyst and that with the titanium catalyst.
TABLE 2
______________________________________
Test With Antimony Test With Titanium
Time without with 0.4% w
without with 0.4% w
(Hours) PMDA PMDA PMDA PMDA
______________________________________
0 0.653 0.653 0.673 0.673
2 0.717 0.804 0.695 0.845
4 0.754 1.020 0.732 0.982
6 0.813 1.328 0.755 1.350
______________________________________
TABLE 3
______________________________________
Test With
Test With
Antimony Titanium
______________________________________
Polycondensation 267 267
Temp (.degree. C.)
Vacuum (mbar) 1-2 1-2
Polycondensation Time 4h 15' 5h
Final Polycondensation 270 270
Temp (.degree. C.)
Quantity of Catalyst (ppm Me) 219 28
Intrinsic Viscosity (dl/g) 0.670 0.655
Activity (IV.sub.f /hrs* ppm Me) 0.000737 0.0046429
Activity Ti/Activity Sb 6.2980011 --
Terminal Acid Groups (Eq/T) 27.20 21.23
Colour
L* 67.74 70.14
a* -3.03 -2.92
b* -1.52 5.24
______________________________________
Analytical Measurements
The intrinsic viscosity of the polyester resin was measured in solution of
0.5 g of resin in 100 ml of 60/40 mixture by weight of phenol and
tetrachloroethane at 25.degree. C. according to ASTM D4603-86.
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